1. Field of the Invention
The present invention relates to a solid-state imaging device and a method for producing the same.
2. Description of the Related Art
As shown in FIG. 22, a typical solid-state imaging device 110 in the related art includes a device chip 101 and an optical glass 102 bonded to the device chip 101 with a bonding layer 103 therebetween. An electrode pad 105, a back-surface electrode pad 108, and a through-via 107 connecting the electrode pad 105 to the back-surface electrode pad 108 are provided on the periphery of the device chip 101. Thus, the front surface side of the device chip 101 is electrically connected to the back surface side thereof by forming the through-via 107 penetrating through the device chip 101, thereby reducing the size of the solid-state imaging device 110 (refer to, for example, Japanese Unexamined Patent Application Publication No. 2004-207461).
In the above solid-state imaging device 110, an etching mask composed of a resist is formed on the back surface side of a semiconductor substrate of the device chip 101 by a lithography process, and a through-hole 106 is then formed in the semiconductor substrate by dry etching such as reactive ion etching (RIE). The through-via 107 is formed so as to fill the through-hole 106. In forming the etching mask for forming the through-hole 106, a double-sided alignment method is employed in which a mask pattern is formed on the back surface of the device chip 101 using a surface pattern of a light-sensing portion 104, the electrode pad 105, and the like of the device chip 101 as a reference.
However, such a solid-state imaging device in the related art also has the following problems: In order to form a through-hole by dry etching such as RIE, it is necessary to penetrate through a semiconductor substrate having a thickness of several hundred micrometers. Therefore, it takes a long etching time and the throughput decreases, resulting in an increase in cost. Furthermore, it is very difficult to ensure the controllability and reproducibility of the etching, and a desired yield for obtaining a satisfactory through-hole is difficult to achieve.
Furthermore, in a back-surface irradiation-type image sensor, it is necessary to form an opening that is continuous through a supporting substrate and an adhesive layer. Accordingly, the material of the adhesive layer is limited when existing dry etching such as RIE is performed. In addition, the etching process itself is very complex.
Consequently, for LSI chips other than solid-state imaging devices, a technique in which an energy ray such as a laser beam is applied is used in practice in order to form such a through-hole.
However, in practical application of this technique to an image sensor, it is necessary to increase the thickness of a stopper electrode and to form a nickel (Ni) electrode having a thickness of 10 μm or more as the stopper electrode. Accordingly, after the formation of the stopper electrode having such a large thickness, it becomes difficult to form a color filter layer and microlenses because of uneven application due to the difference in level. On the other hand, as shown in FIG. 23A, when a stopper electrode 33 is formed after the formation of microlenses 73, the microlenses 73 are degraded by a chemical (reducing agent) used in a nickel plating process for forming the stopper electrode 33. Furthermore, as shown in FIG. 23B, when the thickness of the stopper electrode 33 is reduced in order to prevent uneven application, it is difficult to stop laser drilling in the middle of the stopper electrode 33 and the laser drilling tends to penetrate through the stopper electrode 33. As a result, the material of the stopper electrode 33 is scattered, resulting in problems such as a short-circuit in the front-surface-side electrode 21 and light shielding due to adhesion of the scattered material of the stopper electrode 33 to the microlenses 73 and a second substrate 31, which is a glass substrate.